Inversion Of Fault Slip Rate And Locking Depth

The northeastern margin of the Tibetan Plateau is the frontier area of the uplift and development of the plateau and the extrusion and extension to the interior of the continent.It is the latest and forming part of the plateau and the natural experimental field for studying the deformation in the interior of the continent.The Haiyuan-Liupanshan tectonic zone is located on the northeastern margin of the Tibetan Plateau.It is the boundary zone between the Tibetan Plateau block,Alxa block and ORDOS block.It is a key area for studying the extrusion and extension movement mechanism of the Tibetan Plateau to the interior of the Chinese continent.The data of paleoearthquake,modern tectonic activity,strain accumulation and seismic activity all showed that this section has seismogenic conditions for strong earthquakes.The accurate study of its crustal deformation pattern is a key link to carry out regional deformation mechanism analysis and seismic risk research.Based on the block and fault back-slip model and the TDEFNODE program,this paper analyzed the surface deformation characteristics of this area through the GNSS velocity field.The fine fault distribution of the Haiyuan-Liupanshan fault zone was considered through the fine block and fault division scheme.Based on the optimal model,the fault activity characteristics and block strain parameters of the Haiyuan-Liupanshan fault zone were obtained,including the slip rate,locking depth and slip rate deficit of the faults.The seismic moment and the rate of moment accumulation in each section of the fault zone were calculated,and the maximum potential earthquake magnitude of the Liupanshan fault was estimated.The characteristics of deformation and strain accumulation in this region were given,and the distribution characteristics of locking and slip rate deficit in each section of the fault zone were discussed.Combining the geological,historical seismic and geophysical data in this region,the seismic risk on the northeastern margin of the Tibetan Plateau was analyzed.The main work and conclusions of this paper are as follows:(1)Based on the encrypted GNSS stations around the Haiyuan-Liupanshan fault zone,combining the GNSS velocity field data of the northeastern margin of the Tibetan Plateau from 2010 to 2020,the present horizontal GNSS velocity field was obtained through 459 GNSS observation stations.The surface deformation characteristics of the Haiyuan-Liupanshan fault zone were highlighted by deducting the rotation component of the ORDOS block.(2)The deep deformation and strain parameters of the Haiyuan-Liupanshan fault zone,such as slip rate,locking depth,slip rate deficit,internal block strain parameter and seismic moment accumulation rate were obtained.The Laohushan fault is mainly controlled by sinistral strike-slip with a rate of 3.5mm/yr,an overall locking depth of 5km,and a strong locking depth within 1km.The Haiyuan fault is mainly controlled by sinistral strike-slip with the rate of 3.2mm/yr in the west section,3.0mm/yr in the middle section and 3.2mm/yr in the east section,the locking depth is 10 km,13km and 10 km respectively.The locking degree is weak in the west section and east section,and strong in the middle section.The Liupanshan fault is mainly controlled by thrust extrusion with the rate of 1.9mm/yr in the north section and 1.8mm/yr in the south section,and the overall locking depth is 15 km.The locking degree of the fault is the strongest and evenly distributed on the fault surface,and the locking degree of the south section is slightly stronger than the north section.The Guguan-Baoji fault has both left-lateral strike-slip and thrust extrusion components.The strike-slip rate is1.3-1.4mm/yr,the extrusion rate is 1.2-1.3mm/yr,the overall locking depth of the fault is10 km,and the slip rate deficit decreases from 1.8mm/yr to 0.2mm/yr from west to east.(3)Combined with regional geology,historical seismic data,deep and shallow geophysical data and fault activity characteristics,it is considered that the Liupanshan fault has a high seismic risk.Since the release of earthquake energy in 1921,the Liupanshan fault has accumulated up to Mw6.7 earthquake energy.The Haiyuan fault is still in the post-earthquake stress adjustment stage,and the strain accumulation capacity is considered low.The Laohushan fault has the phenomenon of "shallow creep slip".The main innovations of this paper are as follows:(1)Based on the existing observations on the northeastern margin of the Tibetan Plateau,the data of continuous observation stations in the near-field of the Liupanshan fault zone were added,and the rotation of the ORDOS block was deducted to obtain relatively fine motion distribution characteristics in the region.(2)Considering the fine fault distribution of the Haiyuan-Liupanshan fault zone,when constructing the block and fault model,integrating the surface traces and 3D geometry of the active fault,the fine features of the 3D structure of the fault were considered,and the optimal fault geometry model and parameter setting were obtained through large amounts of calculations.(3)We comprehensively considered the slip distribution characteristics of faults in the Haiyuan-Liupanshan tectonic zone,including the Laohushan Fault,the Haiyuan Fault,the Liupanshan Fault,the Guguan-Baoji Fault,and the spatial differences of the slip characteristics was discussed,which provides a scientific reference for understanding the regional seismogenic mechanism and studying and judging the medium and mid-long term seismic risk.